Photooxidation histidine residues

The rate of phosphoprotein formation in the presence of 5 mM CaCl2 was only slightly affected by mild photooxidation in the presence of Rose Bengal, but the hydrolysis of phosphoenzyme intermediate was inhibited sufficiently to account for the inhibition of ATP hydrolysis [359]. The extent of inhibition was similar whether the turnover of E P was followed after chelation of Ca with EGTA, or after the addition of large excess of unlabeled ATP. These observations point to the participation of functionally important histidine residues in the hydrolysis of phosphoprotein intermediate [359]. 

In the catalysis of the lyase from C. perfringens, the participation of lysine residues forming intennediary Schiff bases between enzyme and substrate molecules, and of histidine residues, has been demonstrated with the aid of photooxidation, reagents for histidine modification, and borohydride reduction in the presence of substrate.408-418 Thus, according to Frazi and coworkers,414 the lyase belongs to the class I lyases (aldolases). The catalytic mechanism proposed is outlined in Scheme 3. Evidence has been educed for the existence of a similar mechanism of cleavage of sialic acid by the lyase enriched from pig kidney.411... 

Inactivated by photooxidation in the presence of methylene blue (60), riboflavine (60), or Rose Bengal (61). Together with the inactivation the concomitant loss of histidine residues is observed. One (probably His 92) or more histidine residues might participate in the enzyme activity. 

Photooxidation of alkaline phosphatase in the presence of methylene blue and Rose Bengal causes loss of activity for both native and apo-enzyme. In the case of the native enzyme, zinc protects 2 to 3 of the 16 histidine residues. The rate of oxidation of tryptophan is not affected by zinc, and there was no loss of tyrosine. Also, photooxidation of the apoenzyme diminishes zinc binding. It would appear that histidine residues play a role in binding the two zinc ions necessary for enzymic activity (91). 

The histidine residue in position 12 is crucial for activity. Its destruction by photooxidation or modification by iodination (No. 13, Table XIB) or carboxymethylation in the 3 position on the ring (No. 24, Table XIA) all destroy potential activity. The first two also substantially lower the association constant while the latter has no effect or may even increase it slightly. The CM group in the 3 position is, of course, easily accommodated and the interaction of the free carboxyl group with other positive charges nearby, e.g., His 119, may explain the increase in association constant. Conversion to a pyrazolyl residue destroys activity but not binding (No. 19). 

In view of the strong photooxidizing properties of [Re(CO)3(phen)(im)]+, aznrin from Pseudomonas aeruginosa has been modified with a rhenium(I) dumine unit via a histidine residue to give... 

Accordingly, Hammett constants or combinations of the argnments a and b can be used to estimate both complex stabilities of substituted aromatics with donor site atoms other than C in biology/biochemistry. Therefore the connection between the rest of the protein and tyrosine phenolate, tryptophan indole or histidine imidazole moieties is taken to be one huge substituent (e.g. in the frequent cases where three histidine residues coordinate to one copper or zinc ion or with tyrosine residues in water photooxidation), possibly introducing charge effects by pH, phosphorylation ( P switch ) or by complexation of other metals like Ca on the outer periphery of the molecule. 

T. Murachi and K. Okumura. Normal apparent pKa value for the ionization of the histidine residue of papain and stem bromelain as determined by photooxidation reaction. FEBS Lett. 40 127 (1974). 

Pyrroles are very sensitive to the action of singlet oxygen ( O2). Wasserman (1970) has observed a novel type of oxidation in the case of aryl-substituted pyrroles exemplified by the photooxidation of 2,3,4,5-tetraphenylpyrrole in methanol. There is special interest in the reactions of imidazoles with O2 since it has been shown that photooxi-dative inactivation of certain enzymes involves destruction of histidine residues, and more specifically oxidation of the imidazole ring (Wasserman and Lenz). These heterocyclic system behave in many respects like furans and pyrroles, but are more prone to cleavage through reactions resembling the oxidation of enamines by 02 (Wasserman et al. 1968). 

Agon V.V., Bubb W.A., Wright A., Hawkins C.L., Davies M.). Sensitizer-mediated photooxidation of histidine residues Evidence for the formation of reactive side-chain peroxides. Free Radical Biology... 

Crystalline pancreatic ribonuclease has a molecular weight of 14,000 and consists of 124 amino acid residues in a single chain, cross-linked by four cystine disulfide bridges (161, 168). The enzyme can be inactivated by photooxidation, presumably by destruction of histidine residues in ri-... 

Y. Okumura and T. Murachi. Photooxidation of histidine and tryptophan residues of papain in the presence of methylene blue. Y. Biochem. 77 913 (1975). 

Dye-sensitized photooxidation with visible light to identify residues critically involved in the biological activity of enzymes has been introduced by Weil et al. (425). The procedure is mild and moderately selective for some amino acid side chains in addition to tryptophan, tyrosine, histidine, methionine, cysteine and cystine are also photooxidizable. It has been found possible, by an appropriate choice of dye, to bring about specific modification of a particular residue. There is, however, considerable variation in the effects of different dyes and of particular experimental conditions [see ref. 112, 255, 319, 426) for reviews]. 

---